Generally, ink jet recording apparatuses that function as image forming apparatuses include an ink cartridge including an ink containing section that contains an ink absorbing body. The ink absorbing body is made of a polymer elastic porous material, such as a polyether-based urethane foam (expandable foam).
The porous material of the ink absorbing body is soaked with ink, and the ink absorbing body is contained in a compressed state in the ink containing section. The ink retained in the porous material is ejected by a capillary action from the ink cartridge to an ink ejecting section via a nozzle, the nozzle being an ink supplying throat provided on the ink containing section.
U.S. Pat. No. 5,182,579 (Date of Patent: Jan. 26, 1993), for example, suggests that the following expression be satisfied as a condition required for such an ink absorbing body:100≦N·R≦200where N is the number of pores per inch (cell density) in the ink absorbing body before the ink absorbing body is contained in the ink containing section (here, N is no larger than 60); and R is the compression ratio (compressibility), which is a volume ratio of the ink absorbing body when it is contained in a compressed state in the ink containing section to the ink absorbing body before it is contained in the ink containing section.
By satisfying the condition above, the ink absorbing body can have required properties for an ink jet cartridge. Such properties include an ability of the ink to perform continuous recording, an ability of the ink to recover, and an ability of the ink to move easily. Such an ink absorbing body is effective even if the porous material is not uniform. Therefore, it is possible to save manufacture cost.
However, a drawback of the foregoing publication is that the ink cartridge cannot use an ink absorbing body whose N·R is greater than 200. This has limited an available range of ink absorbing bodies.
Moreover, the ink cartridge described in the publication above does not consider the properties of the ink absorbed in the ink absorbing body. As a result, depending on the type of the ink used, problems are caused in the ink jet recording apparatus in that the ink is depleted when continuous ejection is performed, and that ink leakage is caused when the ink cartridge is inserted or detached.